Root‐Growth‐Inspired Self‐Morphology‐Evolution of Microsized Bismuth Surrounded by Microsized Hard Carbon for Stabilized Sodium‐Ion Storage

Abstract Alloy‐type materials are desirable for high‐energy sodium‐ion batteries. Different from nanoengineering with pre‐reserving void space and confined carbon coatings, microsized particles promise high specific/volumetric capacities, easy manufacturing, and low cost but are prone to rapid capacity loss. Herein, inspired by the process of “root growth in soil”, microsized Bi particles (µm‐Bi, as “seeds”) surrounded by microsized hard carbon particles (µm‐HC, as “soil”) are ingeniously dispersed through a simple mixing approach. This design utilizes the morphological self‐evolution of µm‐Bi into Bi‐nanonetworks between dispersed µm‐HC during repeated (de)sodiations, leading to a stable capacity retention of 99.8% for 2000 cycles, higher than that of the µm‐Bi electrode (7.2%) at a high mass loading of 5.5 mg cm⁻². The interconnected Bi‐nanonetworks and µm‐HC particles provide continuous electron pathways and facilitate electrolyte infiltration, which effectively boosts electrical contact, stable cycling, and high‐rate capability. Especially, the hybrid Bi₄₀HC₆₀ (optimized weight ratio) thick‐film electrode shows boosted comprehensive electrochemical performance, superior to HC and µm‐Bi electrodes. The Bi₄₀HC₆₀||Na₃V₂(PO₄)₃ full cell, assembled without any pre‐treatment, delivers 4500 stable cycles. This nature‐inspired strategy provides a simple yet practical approach for employing the electrochemically driven evolution of micro‐sized active materials and realizing high specific/volumetric capacities, fast kinetics, and long‐term cycling stability.